Low cost metal salts have been disclosed as useful in heat storage compositions. U.S. Pat. No. 3,986,969 has disclosed compounds of sodium, potassium, magnesium, aluminum, and iron for this purpose. Preferably, the compounds are in the form of chlorides, nitrates, sulfates, phosphates, and carbonates. Sodium carbonate decahydrate and disodium phosphate dodecahydrate are mentioned specifically. Sodium sulfate decahydrate is one of the preferred compounds disclosed in U.S. Pat. No. 3,986,969; and the technical performance data of sodium sulfate decahydrate as a thermal energy storage medium is provided in the bulletin from the Institute of Energy Conversion at the University of Delaware, dated Dec. 1, 1977.
In U.S. Pat. No. 4,263,365 sodium sulfate decahydrate, sodium carbonate decahydrate, and sodium tetraborate are described as being useful in compositions for the preparation of panels to be used in fire-resistant safes.
In order that the heat storage compositions can provide the necessary protection against damage caused by heat and fire, the compositions must be stable when heated; and the compositions must have an isothermal plateau below 125.degree. F., and preferably below 100.degree. F. to protect such objects as floppy disks and other electronic records as well as microfilm, microfiche, and the like. The prior art compositions have contained stabilizers, nucleating agents, thixotropic agents, cementitious materials, cellulose fibers, polyolefin fibers, and other additives so that the compositions could be used as heat storage media. However, in spite of the presence of these additives, many of the prior art compositions do not have the thermo physical properties to protect floppy disks and other electronic records in safes or other storage containers by maintaining the temperature in the storage containers sufficiently low to prevent damage caused by heat from fire.